10=f^2-9f-4

Solution for 10=f^2-9f-4 equation:

10=f^2-9f-4

We move all terms to the left:

10-(f^2-9f-4)=0

We get rid of parentheses

-f^2+9f+4+10=0

We add all the numbers together, and all the variables

-1f^2+9f+14=0

a = -1; b = 9; c = +14;
Δ = b2-4ac
Δ = 92-4·(-1)·14
Δ = 137
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-\sqrt{137}}{2*-1}=\frac{-9-\sqrt{137}}{-2}
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+\sqrt{137}}{2*-1}=\frac{-9+\sqrt{137}}{-2}
$